This invention relates to the manufacture of magnetic transducing heads.
Magnetic transducing heads commonly have a pair of pole pieces separated by a non-magnetic operating gap. In use a recording medium is moved relative to the head and the gap sweeps out a track on which information is recorded or from which information is reproduced.
It is desirable to manufacture the pole pieces and gap as accurately as possible in order to control the width and position of the track. It has been proposed, in British Patent Specification No. 1,164,754, to use a mask which covers part of the gap and the surrounding material of the pole pieces and exposes another part and the surrounding material. The exposed material is removed by, for example, sand blasting, and the mask is then removed. The parts which it had covered remain and form the pole pieces with the operating gap. The configuration of the head is thus determined by the form of the mask rather than the accuracy with which the constituent pieces of the pole pieces are assembled.
We have, however, discovered that the edge of the mask tends to erode, making the size of the recesses formed by the abrasion rather larger than the corresponding openings in the mask as initially applied to the structure. And in addition it is difficult to make masks of a precisely determined size and shape. Consequently the size of the operating gap will not be precisely that of the corresponding part of the mask as initially formed. These inaccuracies can be significant with, for example, the small heads and high track packing densities currently used in digital recording.